Human Body Tissues


Human body tissue is another way of describing how our cells are grouped together in a highly organized manner according to specific structure and function. These groupings of cells form tissues, which then make up organs and various parts of the body. For example, it's easy to see and feel muscle in the body. Muscle is one of the four types of human body tissue. In this lesson, learn more about the types of tissue and how each functions for a different purpose. If you were to try to explain to someone what your body is made of, you might say two arms, two legs, feet and hands, a head and a torso. Or, you might go to the other extreme and say that you are made up of billions of cells. Both answers would be correct. However, there is a more specific way to describe what makes up a body. We are composed of several different types of human body tissue.


Types Of Human Body Tissue:

Epithelial Tissue:
Epithelial tissue is made up of a layer or layers of tightly packed cells that line the surfaces of the body. The largest example of epithelial tissue (also the largest organ in the human body) is the skin. Mammalian skin consists of stratified epithelium, which has several layers of cells. The outermost layers of cells, called squamous cells, are flat plate-like cells, while the deeper layers are roughly cube shaped and called cuboidal cells. Epithelial tissue has multiple functions, but it serves primarily to protect, absorb, and secrete. As you probably already know, our skin organ covers our entire body and protects underlying tissues from bacteria, chemicals, and other injury. Epithelial cells also line the small intestine where they absorb nutrients, and similar cells in the glands secrete enzymes and hormones.


Muscle Tissue: 
Muscle tissue  encompasses not only the muscles, such as those in our legs or fingers, that we actively control, but also the tissue that forms most of our internal organs. There are three types of muscle tissue: skeletal, cardiac, and smooth. Skeletal muscle tissue forms what we think of as our muscles; it is attached to our bones by our tendons and can be relaxed or contracted voluntarily. Similar in structure to skeletal muscle, cardiac muscle is found exclusively in the walls of the heart. The major difference, however, is that cardiac muscle is involuntary and cannot be actively controlled. Similarly, smooth muscle, which forms the muscle layers in internal organs such as the digestive tract and bladder, is an involuntary tissue. Smooth muscle tissue controls slow involuntary movements such as stomach wall contractions and the contractions of arteries to regulate blood flow.


Nervous Tissue:
Nervous tissue  is made up of the nerve cells (neurons) that form the nervous system, including the brain and spinal cord. These cells are especially responsive to stimuli, allowing nervous tissue to transmit stimuli from the brain to the body extremely rapidly.

Connective tissue: 
Connective tissue connects, supports, or separates other tissues and organs. Connective tissue proper, a form of connective tissue, can be either loose or dense. Adipose tissue, or fat, is loose connective tissue, while tendons and ligaments, composed of collagen, are examples of dense connective tissue. Other forms of connective tissue include blood (fluid connective tissue) and cartilage and bone (both forms of supporting connective tissue).

Embryonic Origin of Tissues:

The zygote, or fertilized egg, is a single cell formed by the fusion of an egg and sperm. After fertilization the zygote gives rise to rapid mitotic cycles, generating many cells to form the embryo. The first embryonic cells generated have the ability to differentiate into any type of cell in the body and, as such, are called totipotent, meaning each has the capacity to divide, differentiate, and develop into a new organism. As cell proliferation progresses, three major cell lineages are established within the embryo. Each of these lineages of embryonic cells forms the distinct germ layers from which all the tissues and organs of the human body eventually form. Each germ layer is identified by its relative position: ectoderm (ecto- = “outer”), mesoderm (meso- = “middle”), and endoderm (endo- = “inner”).

Tissue Membranes:

tissue membrane is a thin layer or sheet of cells that covers the outside of the body (for example, skin), the organs (for example, pericardium), internal passageways that lead to the exterior of the body (for example, abdominal mesenteries), and the lining of the moveable joint cavities. There are two basic types of tissue membranes: connective tissue and epithelial membranes

Connective Tissue Membranes:

The connective tissue membrane is formed solely from connective tissue. These membranes encapsulate organs, such as the kidneys, and line our movable joints. A synovial membrane is a type of connective tissue membrane that lines the cavity of a freely movable joint. For example, synovial membranes surround the joints of the shoulder, elbow, and knee. Fibroblasts in the inner layer of the synovial membrane release hyaluronan into the joint cavity. The hyaluronan effectively traps available water to form the synovial fluid, a natural lubricant that enables the bones of a joint to move freely against one another without much friction. This synovial fluid readily exchanges water and nutrients with blood, as do all body fluids.

Epithelial Membranes:

The epithelial membrane is composed of epithelium attached to a layer of connective tissue, for example, your skin. The mucous membrane is also a composite of connective and epithelial tissues. Sometimes called mucosae, these epithelial membranes line the body cavities and hollow passageways that open to the external environment, and include the digestive, respiratory, excretory, and reproductive tracts. Mucous, produced by the epithelial exocrine glands, covers the epithelial layer. The underlying connective tissue, called the lamina propria(literally “own layer”), help support the fragile epithelial layer.
serous membrane is an epithelial membrane composed of mesodermally derived epithelium called the mesothelium that is supported by connective tissue. These membranes line the coelomic cavities of the body, that is, those cavities that do not open to the outside, and they cover the organs located within those cavities. They are essentially membranous bags, with mesothelium lining the inside and connective tissue on the outside. Serous fluid secreted by the cells of the thin squamous mesothelium lubricates the membrane and reduces abrasion and friction between organs. Serous membranes are identified according locations. Three serous membranes line the thoracic cavity; the two pleura that cover the lungs and the pericardium that covers the heart. A fourth, the peritoneum, is the serous membrane in the abdominal cavity that covers abdominal organs and forms double sheets of mesenteries that suspend many of the digestive organs. The skin is an epithelial membrane also called the cutaneous membrane. It is a stratified squamous epithelial membrane resting on top of connective tissue. The apical surface of this membrane is exposed to the external environment and is covered with dead, keratinized cells that help protect the body from desiccation and pathogens.



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